The ALT and AST tests measure enzymes that your liver releases in response to damage or disease. The albumin test measures how well the liver creates albumin, while the bilirubin test measures how well it disposes of bilirubin. ALP can be used to evaluate the bile duct system of the liver.

Having abnormal results on any of these liver tests typically requires follow up to determine the cause of the abnormalities. Even mildly elevated results can be associated with liver disease. However, these enzymes can also be found in other places besides the liver.

Talk to your doctor about the results of your liver function test and what they may mean for you.

Liver function tests are used to measure specific enzymes and proteins in your blood.

Depending on the test, either higher- or lower-than-normal levels of these enzymes or proteins can indicate a problem with your liver.

Some common liver function tests include:

Alanine transaminase (ALT) test

Alanine transaminase (ALT) is used by your body to metabolize protein. If the liver is damaged or not functioning properly, ALT can be released into the blood. This causes ALT levels to increase.

A higher than normal result on this test can be a sign of liver damage.

According to the American College of Gastroenterology, an ALT above 25 IU/L (international units per liter) in females and 33 IU/L in males typically requires further testing and evaluation.

Aspartate aminotransferase (AST) test

Aspartate aminotransferase (AST) is an enzyme found in several parts of your body, including the heart, liver, and muscles. Since AST levels aren’t as specific for liver damage as ALT, it’s usually measured together with ALT to check for liver problems.

When the liver is damaged, AST can be released into the bloodstream. A high result on an AST test might indicate a problem with the liver or muscles.

The normal range for AST is typically up to 40 IU/L in adults and may be higher in infants and young children.

Alkaline phosphatase (ALP) test

Alkaline phosphatase (ALP) is an enzyme found in your bones, bile ducts, and liver. An ALP test is typically ordered in combination with several other tests.

Children and adolescents may have elevated levels of ALP because their bones are growing. Pregnancy can also raise ALP levels. The normal range for ALP is typically up to 120 U/L in adults.

Albumin test

Albumin is the main protein made by your liver. It performs many important bodily functions. For example, albumin:

stops fluid from leaking out of your blood vessels

nourishes your tissues

transports hormones, vitamins, and other substances throughout your body

An albumin test measures how well your liver is making this particular protein. A low result on this test can indicate that your liver isn’t functioning properly.

The normal range for albumin is 3.5–5.0 grams per deciliter (g/dL). However, low albumin can also be a result of poor nutrition, kidney disease, infection, and inflammation.

Bilirubin test

Bilirubin is a waste product from the breakdown of red blood cells. It’s ordinarily processed by the liver. It passes through the liver before being excreted through your stool.

A damaged liver can’t properly process bilirubin. This leads to an abnormally high level of bilirubin in the blood. A high result on the bilirubin test may indicate that the liver isn’t functioning properly.

The normal range for total bilirubin is typically 0.1–1.2 milligrams per deciliter (mg/dL). There are certain inherited diseases that raise bilirubin levels, but the liver function is normal.

Your doctor may order a liver function test if you’re experiencing symptoms of a liver disorder. The different liver function tests can also monitor the progression or treatment of a disease and test for the side effects of certain medications.

Your doctor will give you complete instructions on how to prepare for the blood sample portion of the test.

Certain medications and foods may affect levels of these enzymes and proteins in your blood. Your doctor may ask you to avoid some types of medications, or they may ask you to avoid eating anything for a period of time before the test. Be sure to continue drinking water prior to the test.

You may want to wear a shirt with sleeves that can easily be rolled up to make it easier to collect the blood sample.

After the test, you can usually leave and go about your life as usual. However, if you feel faint or lightheaded during the blood draw, you should rest before you leave the testing facility.

The results of these tests may not tell your doctor exactly which condition you have or the degree of any liver damage, but they might help your doctor determine the next steps. Your doctor will call you with the results or discuss them with you at a follow-up appointment.

In general, if your results indicate a problem with your liver function, your doctor will review your medications and your past medical history to help determine the cause.

If you drink alcohol heavily, then you’ll need to stop drinking. If your doctor identifies that a medication is causing the elevated liver enzymes, then they’ll advise you to stop the medication.

Your doctor may decide to test you for hepatitis, other infections, or other diseases that can affect the liver. They may also choose to do imaging, like an ultrasound or CT scan. They may recommend a liver biopsy to evaluate the liver for fibrosis, fatty liver disease, or other liver conditions.

Medically reviewed by Judith Marcin, MD on July 30, 2018 — Written by Brian Krans and Jacquelyn Cafasso